1. Technical Field
The present invention relates to an axial seal structure and a rotation mechanism provided with the axial seal structure that restricts the flow of a fluid in an axial direction wherein multiple thin sheet seal pieces are arranged at minute intervals in a circumferential direction around the rotating shaft.
Priority is claimed on Japanese Patent Application No. 2010-143765, filed Jun. 24, 2010, the content of which is incorporated herein by reference.
2. Description of the Related Art
An axial seal structure is provided around the axis of a rotating shaft of rotation mechanisms, such as a gas turbine and a steam turbine, in order to reduce the leakage amount of a working fluid that flows from a high pressure side to a low pressure side. As an example of this axial seal structure, an axial seal structure described in the following Patent Document 1 is known, for example.
This axial seal structure is provided with multiple thin sheet seal pieces. In this axial seal structure, multiple thin sheet seal pieces are arranged around the rotating shaft with minute gaps from each other in the circumferential direction such that their respective thickness direction faces the circumferential direction of the rotating shaft. The respective thin sheet seal pieces are arranged in an inclined manner so that their radial inner ends are located closer to the rotational direction side of the rotating shaft rather than their radial outer ends.
In the above axial seal structure, the radial inner ends of the respective thin sheet seal pieces are free ends, and contact the rotating shaft when the rotating shaft remains stationary. However, if the rotating shaft rotates, the radial inner ends of the respective thin sheet seal pieces are floated from the outer peripheral surface of the rotating shaft by a dynamic pressure effect produced by the rotation of the rotating shaft, and are brought into a non-contact state with the rotating shaft. For this reason, in the above axial seal structure, wear of the respective thin sheet seal pieces is suppressed, and the lifespan of the seals becomes long.
Incidentally, a floating force for the respective thin sheet seal pieces is influenced by the presence of gaps between high-pressure-side edges of the respective thin sheet seal pieces and a high-pressure-side fixing member that is fixed to a casing and faces the high-pressure-side edges. The working fluid on the high pressure side basically leaks to the low pressure side through the minute gaps between the thin sheet seal pieces. In this case, the working fluid of the high pressure side flows radially outward through the gaps between the high-pressure-side edges of the respective thin sheet seal pieces and the high pressure side fixing member that is a portion of the casing while going to the low pressure side, and enters the minute gaps between the respective thin sheet seal pieces from the radial outside. Then, the working fluid that has entered the minute gaps flows radially inward while going to the low pressure side. For this reason, the flow of the working fluid in the minute gaps of the respective thin sheet seal pieces acts as a force that offsets a radial outward force for the respective thin sheet seal pieces produced by the aforementioned dynamic pressure effect.
Thus, in the above axial seal structure, as high-pressure-side regulating device for regulating the flow of the working fluid from the high pressure side to the minute gaps of the respective thin sheet seal pieces, a flexible plate is arranged at the gaps between the high-pressure-side faces of the respective thin sheet seal pieces and the high pressure side fixing member, and a floating force for the respective thin sheet seal pieces is secured.
Incidentally, the gap between the inner peripheral edge of the above flexible plate and the outer peripheral surface of the rotating shaft is preferably formed as small as possible in order to regulate the flow of the working fluid from the high pressure side to the minute gaps of the respective thin sheet seal pieces. However, if the contact between the flexible plate and the rotating shaft during vibration or eccentric rotation is taken into consideration, it is preferable to have a certain size.
Thus, in the above axial seal structure, multiple slits are formed on the inner peripheral side of the flexible plate, the flexibility is enhanced closer to the inner peripheral side of the flexible plate than the outer peripheral side thereof, and the gap between the inner peripheral edge of the flexible plate and the outer peripheral surface of the rotating shaft is formed small. Therefore, the flow of the working fluid from the high pressure side to the minute gaps of the respective thin sheet seal pieces is regulated, while avoiding damage or the like of the flexible plate, by deforming the inner peripheral side of the flexible plate even if the flexible plate contacts the rotating shaft during vibration or eccentric rotation.